LCD with selective transmission filter having light transmittance of 80% or more at wavelength regions of 440+/−20nm; 525+/−25nm and 565+/−45nm, and 10% or less at 470 to 485nm and 575 to 595nm

ABSTRACT

A liquid crystal display having a wide color reproduction range is provided. A liquid crystal display includes a liquid crystal panel driven based on image signals, a light source emitting light for illuminating the liquid crystal panel, and a light selective transmission filter, which has wavelength selective transmission characteristics corresponding to spectral characteristics of the light source, selectively transmits light generated from the light source in the specific wavelength regions based on the wavelength selective transmission characteristics, and guides the transmitted light to the liquid crystal panel.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2004-258831 filed in the Japanese Patent Office on Sep.6, 2005, the entire contents of which being incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display displayingimages by utilizing a light source arranged behind a liquid crystalpanel.

2. Description of the Related Art

In these years, the cathode ray tube (CRT), which has been traditionallya mainstream of displays has been replaced by the liquid crystaldisplay, since the liquid crystal display has advantages such as lowpower consumption, space-saving feature, and low cost.

There are several types of liquid crystal displays when categorized by,for example, illumination methods in displaying images. As arepresentative example, a transmissive liquid crystal display, whichdisplays images by utilizing a light source arranged behind a liquidcrystal panel can be cited.

FIG. 1 shows a cross sectional structure of a traditional transmissiveliquid crystal display. A liquid crystal display 91 mainly includes aliquid crystal panel 92, a luminaire 94 (so-called backlight) arrangedbehind the liquid crystal panel 92 (that is, opposite side of theobserver side), and a diffusion sheet 931 arranged therebetween.

The liquid crystal panel 92 mainly includes a polarizing plate 920, aglass substrate 921, a color filter 922, a transparent electrode 923, anorientation film 924, a liquid crystal layer 925, an orientation film926, a transparent pixel electrode 927, a glass substrate 928, and apolarizing plate 929 in this order from the observer side.

Here, in the color filter 922, color filters for respectivelycolor-separating light emitted from the luminaire 94 into, for example,three primary colors of red (R), green (G), and blue (B) are arranged.FIG. 2 shows transmission characteristics of a general color filter. InFIG. 2, the horizontal axis represents wavelengths (nm) of incidentlight, and the vertical axis represents normalized transmittance.Reference symbols B9, G9, and R9 represent transmission characteristicsof the color filter to blue light, green light, and red light,respectively.

For the luminaire 94, a cold-cathode fluorescent lamp 943 called CCFL isgenerally used as a light source. In addition, the luminaire 94 mainlyincludes a prism sheet 941, a diffusion sheet 942, a lamp reflector 944,a light guide plate 945, and a reflective sheet 946. FIG. 3 shows alight source spectrum of a general cold-cathode fluorescent lamp. InFIG. 3, the horizontal axis represents wavelengths (nm) of emittedlight, and the vertical axis represents normalized spectral intensity.Reference symbols B10, G10, and R10 respectively represent peaks of bluelight, green light, and red light. In addition, as a light source, alight emitting diode (LED) or the like may be used.

Here, light emitted from the cold-cathode fluorescent lamp 943 isreflected by the lamp reflector 944 and the reflective sheet 946,directed in the direction of the liquid crystal panel 92, spread overthe whole area of the liquid crystal panel 92 by the light guide plate945, evenly diffused by the diffusion sheets 942 and 931, oriented bythe prism sheet 941, and emitted to the liquid crystal panel 92.

The light enters the liquid crystal panel 92, light with a light volumeaccording to the voltage applied by an unshown driving circuit istransmitted to the observer side for every pixel. In general, the colorfilter having transmission characteristics as shown in FIG. 2 is used toperform color display.

For example, in Japanese Unexamined Patent Application Publication No.2003-279988, a transmissive liquid crystal display capable of securingvisibility to a certain degree even when used in the light environmentby using a CCFL or an LED as a light source is disclosed.

SUMMARY OF THE INVENTION

However, in the traditional transmissive liquid crystal display asabove, there has been a disadvantage that color reproduction ability isinferior compared to in the CRT.

That is, for example, in the case where the CCFL having the light sourcespectrum as shown in FIG. 3 is used as a light source, light emittedfrom the CCFL includes not only the red light peak R10, the green lightpeak G10, and the blue light peak B10, but also extra peaks 95 and 96.Therefore, when the emitted light having such a light source spectrum iscolor-separated by using the color filter having the transmissioncharacteristics as shown in FIG. 2, the color filter shows thetransmission characteristics with the wide wavelength band as shown inthe reference symbols R9, G9, and B9 in the figure, and therefore it isdifficult to selectively transmit only the specific narrow wavelengthband, in which the red light peak R10, the green light peak G10, and theblue light peak B10 exist, that is, it is difficult to remove the extrapeaks 95, 96 and the like. As a result, the color purity is not able tobe improved, and the color reproduction range is narrow. As one of theindices showing color reproducibility in displays, NTSC (NationalTelevision System Committee) ratio can be cited. NTSC ratio shows anarea of a triangle made of color coordinates belonging to the display asa ratio to an area of a triangle made by NTSC color coordinates. TheNTSC ratio in a general transmissive liquid crystal display is aboutfrom 60 to 70%, which is not sufficient.

As above, in the traditional technique, in which color separation isperformed for light emitted from the light source by only the colorfilter having transmission characteristics with a wide wavelength band,it has been difficult to obtain a liquid crystal display having a widecolor reproduction range.

In view of the foregoing, in the present invention, it is desirable toprovide a liquid crystal display having a wide color reproduction range.

According to an embodiment of the present invention, there is provided afirst liquid crystal display including: a liquid crystal panel drivenbased on image signals; a light source emitting light for illuminatingthe liquid crystal panel; and a light selective transmission filter,which has wavelength selective transmission characteristicscorresponding to spectral characteristics of the light source,selectively transmits light generated from the light source in thespecific wavelength regions based on the wavelength selectivetransmission characteristics, and guides the transmitted light to theliquid crystal panel. In this case, it is preferable that the lightsource has respective intensity peaks at least in a red region, a greenregion, and a blue region, light transmittance in the red region, thegreen region, and the blue region of the light selective transmissionfilter is 80% or more, and the rest of the red, green, and blue regionhas wavelength regions whose light transmittance is 10% or less adjacentto the green region.

Here, “red region,” “green region,” and “blue region” respectively meanwavelength regions of red light, green light, and blue light. Forexample, the red region, the green region, and the blue regionrespectively represent a region centering on 625 nm being 90 nm wide, aregion centering on 545 nm being 50 nm wide, and a region centering on435 nm being 40 nm wide. However, the wavelength region is not limitedthereto, and can be varied according to the light source.

Further, when the light selective transmission filter has a substrateand a light selective transmission layer, which is layered on thesubstrate, it is preferable that the light selective transmission layerhas a structure in which higher refractive index layers and lowerrefractive index layers are alternately layered, and the bottom layerand the top layer of the light selective transmission layer are thehigher refractive index layers. Further, it is preferable that the filmthickness distribution of the light selective transmission layer iswithin ±2% to a given target value. Here, “higher refractive indexlayer” means a layer having a refractive index higher than of “lowerrefractive index layer.” On the contrary, “lower refractive index layer”means a layer having a refractive index lower than of “higher refractiveindex layer.” Further, “film thickness distribution” means filmthickness variation among individuals of the light selectivetransmission layer, and in addition, means film thickness variationaccording to positions in the light selective transmission layer formedto have a certain extensity. Further, “given target value” means atarget value previously set in manufacturing. The given target valueincludes, for example, a design value.

According to an embodiment of the present invention, there is provided asecond liquid crystal display including: a liquid crystal panel drivenbased on image signals; a light source emitting light for illuminatingthe liquid crystal panel; and a light selective reflection filter, whichhas wavelength selective reflection characteristics corresponding tospectral characteristics of the light source, selectively reflects lightgenerated from the light source in the specific wavelength regions basedon the wavelength selective reflection characteristics, and guides thereflected light to the liquid crystal panel. In this case, it ispreferable that the light source has respective intensity peaks at leastin a red region, a green region, and a blue region, light reflectance inthe red region, the green region, and the blue region of the lightselective reflection filter is 80% or more, and the rest of the red,green and blue region has wavelength regions whose light reflectance is10% or less adjacent to the green region.

In the first liquid crystal display according to the embodiment of thepresent invention, in the light selective transmission filter, only thelight in the specific wavelength regions based on the wavelengthtransmission characteristics among the light generated from the lightsource is selectively transmitted and guided to the liquid crystalpanel. That is, harmful wavelength light included in the light generatedfrom the light source (that is, light in the regions other than thespecific wavelength regions) is removed.

In the second liquid crystal display according to the embodiment of thepresent invention, in the light selective reflection filter, only thelight in the specific wavelength regions based on the wavelengthreflection characteristics among the light generated from the lightsource is selectively reflected and guided to the liquid crystal panel.That is, harmful wavelength light included in the light generated fromthe light source (that is, light in the regions other than the specificwavelength regions) is removed.

According to the liquid crystal display of the embodiment of the presentinvention, only the light in the specific wavelength regions among thelight generated from the light source is selectively guided to theliquid crystal panel by using the light selective transmission filter orthe light selective reflection filter having wavelength selectivecharacteristics corresponding to spectral characteristics of the lightsource. Therefore, the color purity of illumination light can beimproved. Thereby, the NTSC ratio can be improved, and the wide colorreproduction range can be secured.

In particular, when the light selective transmission filter, in whichlight transmittance in the red region, the green region, and the blueregion is 80% or more, and the rest of the red, green and blue regionhas wavelength regions whose light transmittance is 10% or less adjacentto the green region is used, the light selective transmission filter isbetter adapted to the light source generating light having a intensitypeaks at least in one of the red region, the green region, and the blueregion, and the color purity of the illumination light can besufficiently improved.

Further, when the prism sheet is provided between the light source andthe liquid crystal panel, and the light selective transmission filter isprovided between the prism sheet and the liquid crystal panel, lightfrom the light source is oriented in the direction of the liquid crystalpanel by the prism sheet, and then transmitted through the lightselective transmission filter. Therefore, incident angles of light tothe light selective transmission filter can be small all together. Inthe result, variation of wavelength shift amounts in transmission lightthrough the light selective transmission filter caused by variation ofincident angles can be inhibited.

Further, in the case, in which the light selective reflection filter isformed by using a light selective reflection layer, when incident anglesof light to the light selective reflection layer vary according to theincident positions, variation of wavelength shift amounts when light isreflected by the light selective reflection layer can be inhibited byforming the light selective reflection layer so that the light selectivereflection layer has a film thickness according to incident angles ineach incident position and so that variation of wavelength of reflectedlight according to the position where light is reflected is inhibited.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing an example of a configuration of atraditional transmissive liquid crystal display;

FIG. 2 is a characteristics view showing transmission characteristics ofa general color filter;

FIG. 3 is a characteristics view showing a light source spectrum of ageneral cold-cathode fluorescent lamp;

FIG. 4 is a cross section showing an example of a configuration of aliquid crystal display according to a first embodiment of the presentinvention;

FIG. 5 is a cross section showing an example of a configuration of alight selective transmission filter shown in FIG. 4;

FIG. 6 is a characteristics view showing transmission characteristics ofthe light selective transmission filter shown in FIG. 4;

FIG. 7 is a characteristics view showing spectral intensity ofillumination light transmitted through the light selective transmissionfilter shown in FIG. 4;

FIG. 8 is a characteristics view showing a color reproduction range ofthe liquid crystal display according to the first embodiment;

FIG. 9 is a characteristics view showing a relation between a filmthickness distribution and NTSC ratios of a light selective transmissionlayer;

FIG. 10 is a cross section showing an example of a configuration of aliquid crystal display according to a first modification;

FIG. 11 is a cross section showing an example of a configuration of aliquid crystal display according to a second modification;

FIG. 12 is a cross section-showing another example of the configurationof the liquid crystal display according to the second modification;

FIG. 13 is a cross section showing an example of a configuration of aliquid crystal display according to a second embodiment of the presentinvention;

FIG. 14 is a cross section showing an example of a configuration of alight selective reflection filter shown in FIG. 13;

FIG. 15 is a characteristics view showing reflection characteristics ofthe light selective reflection filter shown in FIG. 13; and

FIG. 16 is a characteristics view for explaining wavelength change whenlight is reflected by the light selective reflection filter shown inFIG. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Best modes for carrying out the present invention (hereinafter simplyreferred to as embodiment) will be hereinafter described in detail withreference to the drawings.

First Embodiment

FIG. 4 shows a cross sectional structure of a liquid crystal displayaccording to a first embodiment of the present invention. A liquidcrystal display 1 is used as a transmissive liquid crystal display andan active matrix liquid crystal display. The liquid crystal display 1includes a liquid crystal panel 2, a luminaire 4 including a lightsource arranged behind the liquid crystal panel 2, and a diffusion sheet31 and a light selective transmission filter 32 arranged between theliquid crystal panel 2 and the luminaire 4.

The liquid crystal panel 2 has a laminated structure having a liquidcrystal layer 25 between a glass substrate 21 on the observer side and aglass substrate 28 on the luminaire 4 side. Specifically, the liquidcrystal panel 2 has a polarizing plate 20, the glass substrate 21, acolor filter 22, a transparent electrode 23, an orientation film 24, theliquid crystal layer 25, an orientation film 26, a transparent pixelelectrode 27, the glass substrate 28, and a polarizing plate 29 in thisorder from the observer side.

The polarizing plates 20 and 29 are a kind of optical shutter, and letsthrough only light (polarization) in a specific oscillation direction.The polarizing plates 20 and 29 are respectively arranged so that thepolarization axes are different from each other by 90°. Thereby, lightemitted from the luminaire 4 is transmitted or blocked through theliquid crystal layer 25.

The glass substrates 21 and 28 are generally transparent substratestransparent to visible light. Therefore, the material thereof is notlimited to glass as long as the material is transparent to visiblelight. Though not shown, on the glass substrate 28 on the luminaire 4side, an active driving circuit including a TFT (Thin Film Transistor)as a driving device electrically connected to the transparent pixelelectrode 27, wiring and the like is formed.

In the color filter 22, color filters for respectively color-separatinglight emitted from the luminaire 4 into three primary colors of red (R),green (G), and blue (B) are arranged. As described later, in the liquidcrystal display 1 of this embodiment, color separation for light emittedfrom the luminaire 4 is performed by the light selective transmissionfilter 32 in addition to the color filter 22.

The transparent electrode 23 is made of, for example, ITO (Indium TinOxide), and functions as a common opposed electrode.

The orientation films 24 and 26 are made of, for example, a polymericmaterial such as polyimide, and perform orientation for the liquidcrystal.

The liquid crystal layer 25 is made of, for example, TN (TwistedNematic) mode liquid crystal or STN (Super Twisted Nematic) mode liquidcrystal. The liquid crystal layer 25 has a function to transmit or blocklight emitted from the luminaire 4 for every pixel by the voltageapplied from an unshown driving circuit.

The transparent pixel electrode 27 is made of, for example, ITO, andfunctions as an electrode for every pixel.

The luminaire 4 has a laminated structure in which a prism sheet 41, adiffusion sheet 42, a light guide plate 45, and a reflective sheet 46are layered, a cold-cathode fluorescent lamp 43 as a light sourcearranged on the side face of the laminated structure, and alamp-reflector 44 arranged around the cold-cathode fluorescent lamp 43.Part of the lamp reflector 44 is opened toward the foregoing laminatedstructure. As above, the luminaire 4 has a so-called edge light typestructure.

The cold-cathode fluorescent lamp 43 is a so-called CCFL, and a kind offluorescent lamp. As shown in FIG. 3 described above, the light sourcespectrum of a general cold-cathode fluorescent lamp has a wide range ofwavelengths from 400 to 700 nm. In the example shown in the figure,specifically, the blue light peak B10 (=435 nm), the green light peakG10 (=545 nm), and the red light peak R10 (=625 nm) exist, in addition,the extra peak 95 (=490 nm) and the extra peak 96 (580 nm) exist.

The lamp reflector 44 has a function to reflect part of light emittedfrom the cold-cathode fluorescent lamp 43 in the direction of the lightguide plate 45. Thereby, light emitted from the cold-cathode fluorescentlamp 43 can be effectively utilized.

The light guide plate 45 has a function to totally reflect andconcurrently propagate light emitted from the cold-cathode fluorescentlamp 43, and to spread the light over the whole area of the liquidcrystal panel 2. Thereby, light emitted from the cold-cathodefluorescent lamp 43 can be flat light.

The reflective sheet 46 has a function to reflect light to be leakedfrom the light guide plate 45 toward inside of the light guide plate 45.Thereby, as in the foregoing lamp reflector 44, light emitted from thecold-cathode fluorescent lamp 43 can be effectively utilized.

The diffusion sheet 42 has a function to diffuse flat light spread overthe whole area of the liquid crystal panel 2 by the light guide plate 45and to reduce brightness unevenness. Thereby, the whole area of theliquid crystal panel 2 is irradiated with light with uniform brightness.

The prism sheet 41 has a function to orient light whose brightness isuniformalized on the whole area of the liquid crystal panel 2 by thediffusion sheet 42 all together in the direction of the liquid crystalpanel 2. Therefore, in the case where the light selective transmissionfilter 32 is provided between the prism sheet 41 and the liquid crystalpanel 2 as in the liquid crystal display 1 of this embodiment, lightemitted from the cold-cathode fluorescent lamp 43 is oriented in thedirection of the liquid crystal panel 2 by the prism sheet 41, and thenis transmitted through the light selective transmission filter 32.Therefore, variation of wavelength shift amounts in light transmittedthrough the light selective transmission filter 32 caused by variationof incident angles can be inhibited.

A diffusion sheet 31 has a function to diffuse light emitted from theluminaire 4 and selectively transmitted through the after-mentionedlight selective transmission filter and to reduce brightness unevennessas the diffusion sheet 42.

As shown in after-mentioned FIG. 6, for example, the light selectivetransmission filter 32 has wavelength selective transmissioncharacteristics corresponding to spectral characteristics of thecold-cathode fluorescent lamp 43 as a light source (for example, FIG.3). In FIG. 6, the horizontal axis represents wavelengths (nm) ofincident light, and the vertical axis represents transmittance (%).Reference symbols B1, G1, and R1 represent a blue region (440±20 nm), agreen region (525±25 nm), and a red region (665±45 nm), respectively. Asabove, the light selective transmission filter 32 has a function toselectively transmit light emitted from the cold-cathode fluorescentlamp 43 (for example, three primary color regions including the redlight peak R10, the green light peak G10, and the blue light peak B10 inFIG. 3) in the specific wavelength regions based on the wavelengthselective transmission characteristics and to guide the transmittedlight to the liquid crystal panel 2. For the details of the wavelengthselective transmission characteristics of the light selectivetransmission filter 32, descriptions will be given later. By providingthe light selective transmission filter 32, the color purity ofillumination light can be improved. In the result, as described later,the NTSC ratio can be improved, and the color reproduction range can beexpanded.

FIG. 5 shows a cross sectional structure of the light selectivetransmission filter 32. In the light selective transmission filter 32, alight selective transmission layer 322 is formed on a transparentsubstrate 321. Further, the light selective transmission layer 322 iscomposed of an optical thin film, in which higher refractive indexlayers 322H1 to 322H4 and lower refractive index layers 322L1 to 322L3are alternately layered. The bottom layer and the top layer of the lightselective transmission layer 322 are made of the higher refractive indexlayers (in FIG. 5, the higher refractive index layers 322H1 and 322H4).

The transparent substrate 321 is a section becoming a support of thelight selective transmission layer 322. For example, the transparentsubstrate 321 is made of a polymeric material containing polycarbonate(PC), polyethylene telephthalate (PET), polyethylene naphthalate (PEN),polyether sulfone (PES), or polyolefin (PO).

The light selective transmission layer 322 is a section playing a corerole of the light selective transmission filter 32. As described above,the light selective transmission layer 322 has a function to selectivelytransmit light emitted from the cold-cathode fluorescent lamp 43 in thespecific wavelength region based on the wavelength selectivetransmission characteristics and to guide the transmitted light to theliquid crystal panel 2.

As described later, the light selective transmission layer 322 can beformed by dry process or wet process. In the case of the dry process,the foregoing higher refractive index layers 322H1 to 322H4 includelayers made of, for example, a titanium oxide such as TiO₂ (refractiveindex: 2.38), a niobium oxide such as Nb₂O₅ (refractive index: 2.28), ora tantalum oxide such as Ta₂O₅ (refractive index: 2.10), and theforegoing lower refractive index layers 322L1 to 322L3 include layersmade of, for example, a silicon oxide such as SiO₂ (refractive index:1.46) or magnesium fluoride such as MgF₂ (refractive index: 1.38).Meanwhile, in the case of the wet process, the higher refractive indexlayers 322H1 to 322H4 and the lower refractive index layers 322L1 to322L3 are made of a solvent material or a non-solvent material such as athermosetting resin and a photocurable resin (for example, ultravioletcurable resin). In this case, specifically, as a higher refractive indexlayer, for example, Opster of JSR (JN7102, refractive index: 1.68) canbe used, and as a lower refractive index layer, for example, Opster ofJSR (JN7215, refractive index: 1.41) can be used.

The structure of the light selective transmission layer 322 is notlimited to the seven-layer structure as shown in FIG. 5. It is enoughthat the light selective transmission layer 322 has an odd-numberedlayer structure such as a five-layer structure and a nine-layerstructure, and the bottom layer and the top layer are the higherrefractive index layers as described above.

An example of the whole structure of the light selective transmissionfilter 32 and film thicknesses of the optical multilayer film is asfollows. The transparent substrate 321 is made of PET, the higherrefractive index layer is made of Nb₂O₅ (referred to as H), and thelower refractive index layer is made of SiO₂ (referred to as L). In thelight selective transmission filter 32, PET/H (film thickness: 457 nm)/L(film thickness 94 nm)/H (film thickness: 457 nm)/L (film thickness 94nm)/H (film thickness: 457 nm)/L (film thickness 94 nm)/H (filmthickness: 457 nm) are layered in this order from the transparentsubstrate 321 side.

Next, descriptions will be given of an example of a method of formingthe light selective transmission filter 32 having the foregoingstructure. As described above, since the light selective transmissionfilter 32 can be formed by the dry process or the wet process,descriptions will be given of both the dry process and the wet process.

First, the transparent substrate 321 made of the foregoing polymericmaterial is prepared. Next, by sputtering method or the like in the caseof the dry process, or by spin coating method, dip coating method or thelike in the case of the wet process, the higher refractive index layers322H and the lower refractive index layers 322L respectively made of theforegoing material are alternately layered on the transparent substrate321. Then, as described above, the bottom layer and the top layer areformed from the higher refractive index layers. Consequently, the lightselective transmission filter 32 is formed.

By arranging the light selective transmission filter 32 formed as abovebetween the luminaire 4 and the diffusion sheet 31 shown in FIG. 4, theliquid crystal display 1 of this embodiment can be manufactured.

Next, basic operations when images are displayed in the liquid crystaldisplay 1 manufactured as above will be hereinafter described.

First, in the luminaire 4, light emitted from the cold-cathodeflorescent lamp 43 is reflected by the lamp reflector 44 and thereflective sheet 46, directed in the direction of the liquid crystalpanel 2, spread over the whole area of the liquid crystal panel 2 by thelight guide plate 45, evenly diffused by the diffusion sheet 42,oriented by the prism sheet 41, and emitted.

Next, among the light emitted from the luminaire 4, light in thespecific wavelength regions based on the wavelength selectivetransmission characteristics is selectively transmitted and emitted tothe liquid crystal panel 2 by the light selective transmission filter32.

The selectively transmitted light enters the liquid crystal panel 2,light having a light volume based on the voltage applied for every pixelbetween the transparent pixel electrode 27 and the transparent electrode23 as an opposed electrode is transmitted and color-separated by usingthe color filter 22, and thereby color images are displayed.

Next, optical characteristics of the liquid crystal display 1 of thisembodiment will be described by comparison with of the traditionalliquid crystal display 91 shown in FIG. 1.

Here, as an example of the light selective transmission filter 32, asdescribed above, the light selective transmission filter 32 havingseven-layer structure in which the transparent substrate 321 is made ofPET, the higher refractive index layer is made of Nb₂O₅ (referred to asH), and the lower refractive index layer is made of SiO₂ (referred to asL), and PET/H (film thickness: 457 nm)/L (film thickness 94 nm)/H (filmthickness: 457 nm)/L (film thickness 94 nm)/H (film thickness: 457 nm)/L(film thickness 94 nm)/H (film thickness: 457 nm) are layered in thisorder from the transparent substrate 321 side is used.

FIG. 6 shows transmission characteristics of the light selectivetransmission filter 32.

As shown in the figure, the light selective transmission filter 32 showswavelength selective transmission characteristics to selectivelytransmit light in the specific wavelength regions corresponding to thelight source spectrum of the cold-cathode fluorescent lamp 43 (forexample, three primary color regions including the red light peak R10,the green light peak G10, and the blue light peak B10 in FIG. 3).Specifically, the specific wavelength regions are, for example, the redregion R1, the green region G1, and the red region R1 in the figure. Thetransmittance in such regions is 80% or more. The rest of the red, greenand blue region has wavelength regions having transmittance of 10% orless (specifically, wavelength regions of about from 470 to 485 nm andabout from 575 to 595 nm) adjacent to the green region (specifically,wavelength regions W1 and W2). Therefore, different from the generalcolor filter shown in FIG. 2, transmission characteristics of a narrowwavelength band are shown. Consequently, when light emitted from thecold-cathode fluorescent lamp 43 is previously filtered by using thelight selective transmission filter 32 in addition to the color filter,the color purity of illumination light of the liquid crystal panel 2 canbe improved.

When light emitted from a general cold-cathode fluorescent lamp havingthe light source spectrum as shown in FIG. 3 was actually transmittedthrough the light selective transmission filter 32 in addition to thecolor filter 22 having the general transmission characteristics as shownin FIG. 2 (that is, configuration of the liquid crystal display 1 ofFIG. 4), it was found that the illumination light spectrum as shown inFIG. 7 was obtained. That is, since the extra peaks 95 and 96 in FIG. 3were removed, only a red light peak R2, a green light peak G2, and ablue light peak B2 in FIG. 7 existed, and intensity of light other thanlight in the specific wavelength regions became very small. As above, itwas found that the color purity of illumination light could be actuallyimproved by using the light selective transmission filter 32 havingwavelength selective transmission characteristics, which adapt to lightsource spectral characteristics of the cold-cathode fluorescent lamp 43.

FIG. 8 shows a color reproduction range of the liquid crystal display 1including the light selective transmission filter 32 having suchwavelength selective transmission characteristics, which is shown inNTSC color space. In the figure, reference symbol 51 represents thecolor reproduction range by NTSC color coordinates, reference symbol 52represents the color reproduction range by the traditional liquidcrystal display 91 as shown in FIG. 1 (that is, the display performingcolor separation for light emitted from the cold-cathode fluorescentlamp 943 only by the color filter 922), reference symbol 53 representsthe color reproduction range by the liquid crystal display 1 of thisembodiment (that is, the display performing color separation for lightemitted from the cold-cathode fluorescent lamp 43 by the light selectivetransmission filter 32 in addition to the color filter 22), andreference symbols R3, G3, and B3 represent regions of color coordinatesof red light, green light, and blue light, respectively.

As above, it was found that in the color reproduction range 53 by theliquid crystal display of this embodiment, the color reproduction rangewas expanded compared to the color reproduction range 52 by thetraditional liquid crystal display, and in particular, significanteffects could be obtained in the green light region G3. Further, whenthe NTSC ratios were compared, the NTSC ratio in the traditional liquidcrystal display was 70.7%, meanwhile the NTSC ratio in the liquidcrystal display of this embodiment was 88.0%, which was a very highvalue. As above, by using the light selective transmission filter 32adapted to the light source spectral characteristics of the cold-cathodefluorescent lamp 43, the NTSC ratio can be improved and the colorreproduction range can be expanded.

As shown in FIG. 9, when a relation between the film thicknessdistribution of the light selective transmission layer 322 (filmthickness of the whole optical multilayer film) and NTSC ratios wasexamined, it was found that as long as the film thickness distributionwas within ±2% to a given target value X (point where the film thicknessdistribution is 0%), apparently high NTSC ratios (about 80% or more)were shown compared to the NTSC ratio Y (70.7%) of the traditionalliquid crystal display. It is not particularly difficult to set the filmthickness distribution of the light selective transmission layer 322within ±2% to a given target value in mass production. Therefore, byusing such an optical selective transmissive filter 32, the NTSC ratioof the liquid crystal display can be surely improved at a high yieldratio in mass production as well.

As above, in this embodiment, the light selective transmission filter 32having wavelength selective transmission characteristics correspondingto spectral characteristics of the light source is provided between thecold-cathode fluorescent lamp 43 as a light source and the liquidcrystal panel 2, light emitted from the cold-cathode fluorescent lamp 43in the specific wavelength regions based on the wavelength selectivetransmission characteristics is selectively transmitted and guided tothe liquid crystal panel 2. Therefore, the color purity of illuminationlight of the liquid crystal panel 2 can be improved. In the result, theNTSC ratio can be improved and the color reproduction range can beexpanded.

In particular, the light selective transmission filter 32 in whichtransmittance in the red region R1 (665±45 nm), the green region G1(525±25 nm), and the blue region B1 (440±20 nm) is 80% or more, and therest of the red, green and blue region has wavelength regions whoselight transmittance is 10% or less adjacent to the green region G1 isused. Therefore, the light selective transmission filter 32 is betteradapted to the cold-cathode fluorescent lamp 43 generating light havingintensity peaks in such red region R1, green region G1, and blue regionB1 (for example, the red light peak R10, the green light peak G10, andthe blue light peak B10), and color purity of illumination light can besufficiently improved.

Further, the light selective transmission filter 32 is provided betweenthe prism sheet 41 and the liquid crystal panel 2. Therefore, variationof wavelength shift amounts in the light transmitted through the lightselective transmission filter 32 caused by variation of incident anglescan be inhibited. In the result, the color purity of illumination lightcan be further improved.

Further, the light guide plate 45 is provided in the luminaire 4 toobtain the edge light type structure. Therefore, the whole area of theliquid crystal panel 2 can be irradiated with light emitted from thesingle light source (cold-cathode fluorescent lamp 43), and the liquidcrystal display 1 can be thinned.

Further, when the film thickness distribution of the light selectivetransmission filter 32 is within ±2% to a given target value, the NTSCratio of the liquid crystal display can be surely improved. Therefore,the liquid crystal display can be easily formed at a high yield ratio inmass production.

In the liquid crystal display 1 of this embodiment, the case, in whichthe light selective transmission filter 32 is provided between the prismsheet 41 and the liquid crystal panel 2 has been described. However,arrangement of the light selective transmission filter 32 is not limitedthereto. The light selective transmission filter 32 is preferablyarranged between the cold-cathode fluorescent lamp 43 as a light sourceand the liquid crystal panel 2.

Descriptions will be given of Modification 1 of the first embodiment.

[Modification 1]

In this modification, the light selective transmission filter isarranged on the surface of the cold-cathode fluorescent lamp 43 as alight source in the first embodiment.

FIG. 10 shows a cross sectional structure of a liquid crystal displayaccording to this modification. A liquid crystal display 11 of thismodification includes the liquid crystal panel 2, the luminaire 4arranged behind the liquid crystal panel 2, and the diffusion sheet 31arranged therebetween. The point different from the liquid crystaldisplay 1 in the first embodiment is that a light selective transmissionfilter 33 is arranged on the surface of the cold-cathode fluorescentlamp 43 as a light source as described above. The light selectivetransmission filter 33 is not always directly arranged on the surface ofthe cold-cathode fluorescent lamp 43, but other layer may be sandwichedinbetween. Other respective components are similar to of the firstembodiment, and therefore descriptions thereof are omitted.

When the light selective transmission filter 33 is arranged on thesurface of the cold-cathode fluorescent lamp 43 as a light source asabove, light emitted from the cold-cathode fluorescent lamp 43 in thespecific wavelength regions can be selectively transmitted and guided tothe liquid crystal panel 2, and effects similar to of the firstembodiment can be obtained as well.

As a method of arranging the light selective transmission filter 33 ofthis modification on the surface of the cold-cathode fluorescent lamp43, a method of directly forming the light selective transmission layer322 by the foregoing dry process or the foregoing wet process, or amethod of bonding the light selective transmission filter 32 formed bythe method described in the first embodiment on the surface of thecold-cathode fluorescent lamp 43 by, for example, an adhesive tape.

Next, descriptions will be given of Modification 2 of the firstembodiment.

[Modification 2]

This modification relates to a so-called underlay luminaire, in whichthe cold-cathode fluorescent lamp 43 as a light source is arrangeddirectly under the liquid crystal panel 2 in the first embodiment.

FIG. 11 shows a cross sectional structure of a liquid crystal displayaccording to this modification. A liquid crystal display 12 of thismodification includes the liquid crystal panel 2, the luminaire 4arranged behind the liquid crystal panel 2, the diffusion sheet 31 andthe light selective transmission filter 32, which are arranged betweenthe liquid crystal panel 2 and the luminaire 4. The point different fromthe liquid crystal display 1 in the first embodiment is that theluminaire 4 has a underlay configuration. That is, the luminaire 4 has astructure in which a plurality of cold-cathode fluorescent lamps 43 as alight source (in this modification, the case, in which four cold-cathodefluorescent lamps 43 are arranged is shown) and the lamp reflectors 44,which are arranged around the plurality of cold-cathode fluorescentlamps 43, are arranged directly under a multilayer film having alaminated structure including the prism sheet 41 and the diffusion sheet42 in this order from the observer side. Since the cold-cathodefluorescent lamp 43 is arranged directly under the liquid crystal panel2, the light guide plate 45 is not necessary, and the plurality ofcold-cathode fluorescent lamps 43 can be arranged. Other components aresimilar to of the first embodiment, and therefore descriptions thereofare omitted.

By making the luminaire 4 having the underlay structure as above, thelight guide plate 45 is not necessary. As a result, in addition to theeffects in the first embodiment, the structure can be simplified, andthe number of parts can be decreased. Therefore, the cost can be therebyreduced. Further, since the plurality of cold-cathode fluorescent lamps43 can be arranged, brightness of the liquid crystal display 12 can beimproved.

As shown in FIG. 12, in the underlay luminaire 4, as in the foregoingmodification 1, it is also possible to arrange a light selectivetransmission filter 34 including components indicated by referencesymbols 341 to 344 on the surface of the respective cold-cathodefluorescent lamp 43. In this case, the effects similar to of FIG 11 canbe obtained.

Second Embodiment

Next, descriptions will be given of a second embodiment of the presentinvention.

In the foregoing first embodiment, the liquid crystal display, in whichthe color reproduction range is expanded by providing the lightselective transmission filter has been described. In this embodiment, aliquid crystal display capable of expanding the color reproduction rangeby providing a light selective reflection filter will be described.

FIG. 13 shows a cross sectional structure of the liquid crystal displayaccording to the second embodiment of the present invention. A liquidcrystal display 6 of this embodiment includes the liquid crystal panel2, the luminaire 4 arranged behind the liquid crystal panel 2, and thediffusion sheet 31 arranged therebetween. The point different from theliquid crystal display 1 in the first embodiment is that, as describedabove, instead of the light selective transmission filter, a lightselective reflection filter 36 is provided between a slope K of thelight guide plate 45, that is, the light guide plate 45 and thereflective sheet 46. In other words, the luminaire 4 has a laminatedstructure including the prism sheet 41, the diffusion sheet 42, thelight guide plate 45, the light selective reflection filter 36, and thereflective sheet 46 from the observer side, the cold-cathode fluorescentlamp 43 as a light source arranged on the side face of the laminatedstructure, and the lamp reflector 44 arranged around the cold-cathodefluorescent lamp 43. Part of the lamp reflector 44 is opened toward theforegoing laminated structure as in the first embodiment. The lightselective reflection filter 36 also has a function as a reflectivesheet, and therefore the reflective sheet 46 is not necessarilyprovided. Further, other components are similar to of the firstembodiment, and therefore descriptions thereof are omitted.

For example, as shown in FIG. 15, which will be described later, thelight selective reflection filter 36 has wavelength selective reflectioncharacteristics corresponding to spectral characteristics of thecold-cathode fluorescent lamp 43 as a light source (for example, FIG.3). In FIG. 15, the horizontal axis represents wavelengths (nm) ofincident light, and the vertical axis represents reflectance (%), andreference symbols B4, G4, and R4 represent a blue light region (460±10nm), a green light region (535±10 nm), and a red light region (660±10nm), respectively. As above, the light selective reflection filter 36has a function to selectively reflect light emitted from thecold-cathode fluorescent lamp 43 (for example, three primary colorregions including the red light peak R10, the green light peak G10, andthe blue light peak B10 in FIG. 3) in the specific wavelength regionsbased on the wavelength selective reflection characteristics and toguide the reflected light to the liquid crystal panel 2. The details ofthe wavelength selective reflection characteristics of the lightselective reflection filter 36 will be described later. By providing thelight selective reflection filter 36, the color purity of illuminationlight can be improved. In the result, as described later, the NTSC ratiocan be improved, and the color reproduction range can be expanded.

Though details will be described later, the light selective reflectionfilter 36 has a slope film structure whose film thickness corresponds toincident angles as the light selective reflection filter 36 is arrangedon the slope K so that the incident angles of incident light emittedfrom the cold-cathode fluorescent lamp 43 vary according to incidentpositions. Thereby, variation of wavelength shift amounts when lightemitted from the light source is reflected by the light selectivereflection filter 36 can be inhibited.

FIG. 14 shows a cross sectional structure of the light selectivereflection filter 36 shown in FIG. 13. In the light selective reflectionfilter 36, a light selective reflection layer 362 is formed on a metalsubstrate 361. The light selective reflection layer 362 includes anoptical thin film, in which metal layers 362M1 and 362M2 and dielectriclayers 362D1 and 362D2 are alternately layered.

The metal substrate 361 is a section becoming a support for the lightselective reflection layer 362, and is made of, for example, a metalmaterial such as aluminum (Al).

The light selective reflection layer 362 is a section playing a corerole of the light selective reflection filter 36. As described above,the light selective reflection layer 362 has a function to selectivelyreflect light emitted from the cold-cathode fluorescent lamp 43 in thespecific wavelength regions corresponding to the wavelength selectivereflection characteristics and to guide the reflected light to theliquid crystal panel 2.

As described later, the light selective reflection layer 362 can beformed by the dry process. Further, the foregoing metal layers 362M1 and362M2 include a layer made of, for example, niobium (Nb), aluminum (Al),gold (Au), or silver (Ag). The foregoing dielectric layer 362D1 and362D2 include, for example, a titanium oxide such as TiO₂, a niobiumoxide such as Nb₂O₅, or a tantalum oxide such as Ta₂O₅.

Next, descriptions will be given of an example of a method of formingthe light selective reflection filter 36 with such a structure. Asdescribed above, the light selective transmission filter 32 can beformed by the dry process.

First, the metal substrate 361 made of the foregoing metal material isprepared. Next, for example, by sputtering method, on the metalsubstrate 361, the metal layers 362M and the dielectric layers 362D madeof the foregoing respective materials are alternately layered.Consequently, the light selective reflection filter 36 is formed.

The light selective reflection filter 36 formed as above is arrangedbetween the slope K of the light guide plate 45 shown in FIG. 13, thatis, the light guide plate 45 and the reflective sheet 46, therebymanufacturing the liquid crystal display 6 of this embodiment. However,as described above, when the light selective reflection filter 36 alsohas a function as the reflective sheet 46 and the reflective sheet 46 isnot formed, the light selective reflection filter 36 may be directlyformed over the whole area of the light guide plate 45.

Next, basic operations when images are displayed in the liquid crystaldisplay 6 manufactured as above will be hereinafter described.

First, in the luminaire 4, light emitted from the cold-cathodeflorescent lamp 43 is reflected by the lamp reflector 44, and thereflected light is emitted to the light selective reflection filter 36.Next, among the light emitted from the luminaire 4, light in thespecific wavelength regions based on the wavelength selective reflectioncharacteristics is selectively reflected and emitted in the direction ofthe liquid crystal panel 2 by the light selective reflection filter 36.Next, the selectively reflected light is spread over the whole area ofthe liquid crystal panel 2 by the light guide plate 45, evenly diffusedby the diffusion sheet 42, oriented by the prism sheet 41, and therebyemitted to the liquid crystal panel 2.

The selectively transmitted and emitted light in the luminaire 4 entersthe liquid crystal panel 2, light having a light volume based on thevoltage applied for every pixel between the transparent pixel electrode27 and the transparent electrode 23 as an opposed electrode istransmitted and color-separated by using the color filter 22, andthereby color images are displayed.

Next, optical characteristics of the liquid crystal display 6 of thisembodiment will be described by comparison with of the traditionalliquid crystal display shown in FIG. 1.

FIG. 15 shows reflection characteristics of the light selectivereflection filter 36.

As shown in the figure, the light selective reflection filter 36 showswavelength selective reflection characteristics to selectively reflectlight in the specific wavelength regions corresponding to the lightsource spectrum of the cold-cathode fluorescent lamp 43 (for example,three primary color regions including the red light peak R10, the greenlight peak G10, and the blue light peak B10 in FIG. 3). Specifically,the specific wavelength regions are, for example, the red region R4, thegreen region G4, and the red region R4 in the figure. The reflectance insuch regions is 80% or more. The rest of the red, green and blue regionhas wavelength regions having reflectance of 10% or less (specifically,wavelength regions of about from 475 to 510 m and about from 560 to 615nm) adjacent to the green region G4 (for example, from the blue regionB4 to the red region R4 in the figure). Therefore, different from thetransmission characteristics of a general color filter shown in FIG. 2,reflection characteristics of a narrow wavelength band are shown.Consequently, when light emitted from the cold-cathode fluorescent lamp43 is previously filtered by using the light selective transmissionfilter 32 in addition to the color filter, the color purity ofillumination light of the liquid crystal panel 2 can be improved.Thereby, as in the first embodiment, the NTSC ratio can be improved, andthe color reproduction range can be expanded.

Further, FIG. 16 shows wavelength change when light is reflected by thelight selective reflection filter 36. reference symbols 71 to 74 in thefigure respectively represent reflection characteristics when theincident angles are 0°, 15°, 30°, and 40°.

As above, it was found that as the incident angle was increased from 0°to 40°, a blue light peak B5, a green light peak G5, and a red lightpeak R5 are shifted to the short wavelength side with the intensityunchanged, that is, it was found that when light is reflected by thelight selective reflection filter 36, wavelength is changed according toincident angles.

Therefore, as described above, the light selective reflection filter 36of this embodiment has a slope film structure whose film thicknesscorresponds to incident angles, considering that the light selectivereflection filter 36 is arranged on the slope K so that the incidentangles of incident light emitted from the cold-cathode fluorescent lamp43 vary according to the incident positions as described above. Thereby,variation of wavelengths of reflected light according to the positionwhere light is reflected can be inhibited, and variation of wavelengthshift amounts when light emitted from the light source is reflected bythe light selective reflection filter 36 can be inhibited.

As above, in this embodiment, the light selective reflection filter 36having wavelength selective reflection characteristics corresponding tothe spectral characteristics of the cold-cathode fluorescent lamp 43 asa light source is provided between the slope K of the light guide plate45, that is, the light guide plate 45 and the reflective sheet 46. Amongthe light emitted from the cold-cathode fluorescent lamp 43, light inthe specific wavelength regions based on the wavelength selectivereflection characteristics is selectively reflected, and guided to theliquid crystal panel 2. Therefore, as in the first embodiment, byimproving the color purity of illumination light of the liquid crystalpanel 2, the NTSC ratio is improved and the color reproduction range canbe expanded.

In particular, the light selective reflection filter 36 in whichreflectance in the red region R4 (660±10 nm), the green region G4(535±10 nm), and the blue region B4 (460±10 nm) is 80% or more, and therest of the red, green and blue region has wavelength regions whoselight reflectance is 10% or less adjacent to the green region G4 isused. Therefore, the light selective reflection filter 36 is betteradapted to the cold-cathode fluorescent lamp 43 emitting light havingthe intensity peaks in such red region R4, green region G4, and blueregion B4 (for example, the red light peak R10, the green light peakG10, and the blue light peak B10), and the color purity of illuminationlight can be sufficiently improved.

Further, the light selective reflection filter 36 has a slope filmstructure whose film thickness corresponds to incident angles of lightemitted from the cold-cathode fluorescent lamp 43. Therefore, variationof wavelengths of reflected light according to the position where lightis reflected can be inhibited, and variation of wavelength shift amountswhen light emitted from the light source is reflected by the lightselective reflection filter 36 can be inhibited. In the result, thecolor purity of illumination light can be further improved.

While the invention has been described with reference to the first andthe second embodiments and the modifications, the invention is notlimited to the foregoing embodiments and the like, and variousmodifications may be made.

For example, in the foregoing embodiments and the like, the case, inwhich the cold-cathode fluorescent lamp, which is he CCFL, is used as alight source of the luminaire has been described. However, the luminairecan be composed by using other light source such as an LED.

Further, materials, thicknesses, deposition methods, and depositionconditions of the respective layers are not limited to the materials,thicknesses, deposition methods, and deposition conditions of therespective layers, which have been described in the foregoingembodiments and the like. Other materials, thicknesses, depositionmethods, and deposition conditions may be applied.

Further, in the foregoing embodiments and the like, the configurationsof the liquid crystal display have been described with reference to thespecific examples. However, it is not necessary to provide all layers,or it is possible to provide other layer.

Further, in the foregoing embodiments and the like, the case of theactive matrix liquid crystal display has been described. However, thepresent invention can be applied to the case of a simple matrix drivingliquid crystal display as well.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A liquid crystal display comprising: a liquid crystal panel drivenbased on image signals; a light source emitting light for illuminatingthe liquid crystal panel; and a light selective transmission filter,which has wavelength selective transmission characteristicscorresponding to spectral characteristics of the light source,selectively transmits light generated from the light source in thespecific wavelength regions based on the wavelength selectivetransmission characteristics, and guides the transmitted light to theliquid crystal panel, wherein light from the light source has respectiveintensity peaks at least in a red region, a green region, and a blueregion, light transmittance in the red region, the green region, and theblue region of the light selective transmission filter is 80% or more,and the rest of the red, green and blue region includes wavelengthregions whose light transmittance is 10% or less adjacent to the greenregion, wherein light transmittance of the light selective transmissionfilter in wavelength regions of 440±20 nm, 525±25 nm and 665±45 nm is80% or more, and that in wavelength regions from about 470 to 485 nm andabout 575 to 595 nm is 10% or less.
 2. A liquid crystal displayaccording to claim 1, wherein the light selective transmission filterhas: a substrate; and a light selective transmission layer which islayered on the substrate.
 3. A liquid crystal display according to claim2, wherein the light selective transmission layer has a structure inwhich higher refractive index layers and lower refractive index layersare alternately layered, and the bottom layer and the top layer of thelight selective transmission layer are the higher refractive indexlayers.
 4. A liquid crystal display according to claim 3, wherein a filmthickness distribution of the light selective transmission layer iswithin ±2% to a given target value.
 5. A liquid crystal displayaccording to claim 3, wherein the higher refractive index layers includea layer made of a titanium oxide, a niobium oxide, or a tantalum oxide,and the lower refractive index layers include a layer made of a siliconoxide or magnesium fluoride.
 6. A liquid crystal display according toclaim 3, wherein the higher refractive index layer and the lowerrefractive index layer are made of a thermosetting resin or aphotocurable resin.
 7. A liquid crystal display according to claim 2,wherein the substrate is made of a polymeric material containingpolycarbonate, polyethylene telephthalate, polyethylene naphthalate,polyether sulfone, or polyolefin.
 8. A liquid crystal display accordingto claim 1, further comprising: a prism sheet between the light sourceand the liquid crystal panel, the prism sheet orienting diverged lightfrom the light source in the direction toward the liquid crystal panel,wherein the light selective transmission filter is provided between theprism sheet and the liquid crystal panel.
 9. A liquid crystal displayaccording to claim 1, wherein the light selective transmission filter isformed on the surface of the light source.
 10. A liquid crystal displayaccording to claim 1, wherein the light source is formed of acold-cathode tube.
 11. A liquid crystal display according to claim 1,further comprising a light guide plate which propagates light generatedfrom the light source.